It is known that polyurethanes having good-to-poor properties can be prepared by reacting isocyanate prepolymers with chain extenders and that the properties obtained are at least partly dependent on the particular prepolymer/chain extender combination used to prepare the polyurethane. A disadvantage of known polyurethanes is that even those which have otherwise satisfactory properties do not retain sufficient hardness at elevated temperatures to make them useful in applications where they would be subjected to temperatures in excess of about 175.degree. C.
U.S. Pat. No. 4,595,742 (Nalepa et al.) discloses the utility of aromatic diamines bearing two ar-alkylthio substituents as chain extenders which can be reacted with a variety of isocyanate prepolymers.